The use of hydrostatic drive systems for agricultural and other work machines is well known. The hydrostatic drive utilizes pressurized hydraulic fluid to variably drive a hydraulic motor with a variable displacement hydrostatic pump. The application of this drive to agricultural vehicles is particularly useful in agricultural machines such as self-propelled windrowers. By having a dual path, hydrostatic drive operating wheels at outboard portions of the windrower, a maximum of maneuverability is achieved at the end of the field being harvested to achieve minimum turning radiuses. While such a dual path drive feature adds to the maneuverability of a hydrostatically driven windrower, the variations in pump output can have an impact on the ability of the windrower to track in a straight line and to accelerate in a uniform fashion. This is caused by manufacturing variations in the output of the individual pumps so that one may have a greater or lesser output than the other under varying field conditions or forward speeds.
It has been known in the past to adjust the inputs of hydrostatic pumps by adjusting the linkage of a control rod connected between an operator steering and forward motion mechanism and the radial arms used to vary the output of the hydrostatic pumps. While such an adjustment may allow the matching of the outputs of the pumps at a given pump output RPM, it does not necessarily do so over the entire operating range of the hydrostatic pumps.
The solution to this problem has been disclosed in US Published Patent Application 20100111712 wherein an adjustable control arm assembly is provided for a hydrostatic pump having a pivotal control input shaft. The assembly includes a first arm connected to the pump control input shaft to provide a pivotal input and a second arm connected to an operator displacement input. A mechanism interconnects the first and second arms to provide a selectively adjustable pivotal relationship between the first and second arms. In the design of US 20100111712 the pump displacement was controlled by adjusting a ball stud connected to the control rods vertically up and down relative to a control arm connected to the pump. However, it has been found that with different pumps having different displacements it is sometimes necessary to provide different lengths of control arms. For example, with a higher displacement pump the control arms need to be shorter in order to rotate the controller of the pump while maintaining the same amount of mechanical input from the steering mechanism and hydro handle than with a lower displacement pump. For manufacturers of vehicles and equipment the need to have different sized control arms for different pump sizes is problematic in that the manufacturer must stock additional parts and mistake proofing is complicated by having different sized control arms.
What is needed therefore is a common pump control arm assembly that does not require mistake proofing and provides enough adjustment for the different displacements of various sizes of drive pumps.